With the increasingly extensive use of network technologies, a great variety of networking devices have been developed to suit user needs. For example, one who needs frequent use of broadband services may require an Asymmetric Digital Subscriber Line (ADSL) modem coupled to a central office (CO) line or a cable modem coupled to a TV signal cable in order to make Internet connection. As wireless network technologies gradually mature, cable-based broadband Internet connection has given way to the wireless version by degrees, not only because the latter can be implemented with far less cables than required in the former, but also because one who has made such wireless connection through an electronic device is allowed to move about freely. However, despite the huge convenience it brings to network applications, wireless broadband Internet connection has such drawbacks as low data security and high susceptibility to interruption. To overcome these drawbacks while maintaining the advantage of not requiring additional network cables, the power line communication (PLC) technology was devised and is now available for use. Generally speaking, a power line networking device is advantageous over modems and like networking devices in that it does not require extra cabling work, provides wide network coverage, allows easy connection, and has high data rate. In fact, a power line networking device relies on no more than a household power line to make broadband Internet connection. Therefore, a client end only has to plug a power line networking device to a wall socket, and broadband Internet connection can be established directly through the power line; in other words, there is no need for a broadband network service provider to install additional wires at the client end.
Currently, the major PLC standards are HomePlug AV and G.hn, both of which specify signal transmission via existing wires in a house so that no extra wiring is needed—a chief advantage of PLC over the conventional wired networking methods. In addition, data transmission through power lines will not be hindered by concrete walls or human bodies and therefore features higher stability and less delay than through the conventional wireless networks. In a power line network, it is necessary to choose a certain machine as the central controller, which in the HomePlug AV standard is referred to as the Central Coordinator (CCo), and in the G.hn standard as the Domain Master (DM). The central controller servers to organize the entire power line network, keep the data of the nodes in the power line group, and arrange the order of data transmission. A good central controller is one capable of effectively increasing the efficiency of the power line network and the number of supported nodes in the group. Recently, the trend of digital homes has caused such an increase in the demand for HD video, IP cam, and home automation that it is not uncommon for a house to be equipped with multiple PLC adapters. In order to achieve a balance between the performance and power consumption of products, the number of nodes in a power line group, and, last but not least, costs, it is important to be able to effectively and accurately select the optimal central controller for controlling the entire power line network.
As stated above, a power line network provides relatively stable signal transmission due to the fact that signals are transmitted through physical lines. During signal transmission, however, the data rate may drop because the various parts of the power line network are very likely to be affected by the phases of electricity and the noise of other electrical appliances, depending on the arrangement of power lines and the relative positions of such other electrical appliances. Besides, old wire taps and old wires may also compromise signal transmission efficiency. Therefore, the selection of the central controller should take into account the user's practical needs, the number of nodes each controller in the power line network can support, and the efficiency of connection between each controller and other controllers, among other factors. Only when the central controller is so selected can the performance of the power line network be optimized. Nevertheless, the existing mechanism for selecting the central controller in a power line network is merely to preset the controller that is first turned on as the central controller, without any optimization measures taken to deal with the actual network state. Hence, if the controller that is first turned on is a product of relatively low-end specifications, the number of supported nodes in the network will be relatively small, thus compromising network performance. If the controller that is first turned on is located where significant attenuation tends to occur and where there is strong interference, the stability of signal transmission through the power line network may be reduced.
In a nutshell, a conventional power line network is in want of a mechanism for selecting the optimal central control according to the actual network state and is therefore subject to compromised network performance and unstable signal transmission. The issue to be addressed by the present invention is to design a method for selecting the optimal central controller in a power line network so that the performance of the power line network can be automatically and effectively optimized.